Dart isn't just another javascript abstraction. It has the option to compile into JavaScript, but so do many other independent languages, like Scala, Clojure and Haskell. It is its own language, with a VM, spec, an independent set of libraries, etc. This as opposed to for example CoffeeScript, which is purely (and intentionally) a JavaScript abstraction.
That said, my personal wish would be a language-agnostic virtual machine (or where the only "language" is that of the virtual machine itself) for the DOM, with a well-defined standard that could be implemented by different browsers. This would allow a lot of performance optimizations and remove the need for JavaScript to be a compile target. Instead, JavaScript would simply be one of a number of languages which target this VM.
You mean Java. The JVM was a way to safely run arbitrary code in a browser, write-once-run-anywhere. It was too early to come with DOM APIs to interact with the page around it, instead being like Flash in believing that the useful interactions would be inside the Java applet's window. But if we just took a headless JVM and gave it DOM APIs then problem solved.
That said, my personal wish would be a language-agnostic virtual machine (or where the only "language" is that of the virtual machine itself) for the DOM, with a well-defined standard that could be implemented by different browsers. This would allow a lot of performance optimizations and remove the need for JavaScript to be a compile target. Instead, JavaScript would simply be one of a number of languages which target this VM.